1. Field of the Invention
The present invention relates to an emulsion composition. More particularly, it relates to an emulsion composition which has a long pot-life and can be made into a film having a high wet strength and being excellent in water resistance, hot water resistance and heat resistance, said film being obtained by coating said emulsion composition and thereafter evaporating the water contained therein.
2. Description of Related Arts
The emulsion produced by the use of polyvinyl alcohol as the protective colloid (dispersant) has admirably been used in a variety of applications such as paint coating, adhesive, fiber sizing agent and paper coating since long years before.
However, since polyvinyl alcohol is water-soluble, the film obtained by evaporating the water contained in the above-mentioned emulsion involves the problems as described hereunder.
The film is so insufficient in water resistance that it is liable to swell in water and that it is liable to be eluted when the film is immersed in water. In addition, when the film is immersed in water and the water is boiled, the swelling and elution as mentioned above are accelerated, resulting in failure to maintain the original form of the film.
In many cases, the emulsion shows its performance when it is made into a film. Accordingly, the glass transition temperature of a resin as the dispersoid is adjusted to room temperature or to the extent that film formation is possible by heat treatment in a short time. Thus, the working temperature exceeding the glass transition temperature softens the film and deteriorates its heat resistance.
A variety of attempts have heretofore been made to improve the water resistance, hot water resistance and heat resistance of the film obtained from the emulsion in which polyvinyl alcohol is used as the dispersant.
As an typical example thereof, there is known a method in which an emulsion containing polyvinyl alcohol as the dispersant is blended with a polyvalent isocyanate compound. The method, however, involves the problem of the workability due to the short pot-life of the composition thus obtained.
There are also proposed various adhesives comprising an aqueous emulsion containing polyvinyl alcohol as the dispersant. For example, there are disclosed (1) an adhesive which comprises an aqueous emulsion containing as the dispersant polyvinyl alcohol having a ratio (Mw/Mn) of weight-average molecular weight (Mw) to number-average molecular weight (Mn) of 2.4 or less and a crosslinking agent (Japanese Patent Application Laid-Open No. 108603/1986); (2) an adhesive which comprises an aqueous emulsion containing polyvinyl alcohol as the dispersant and an aliphatic aldehyde such as glyoxal (Japanese Patent Application Laid-Open No. 94937/1980; (3) an adhesive which comprises polyvinyl alcohol, an aqueous emulsion, a crosslinking agent and an amino compound such as chitosan (Japanese Patent Application Laid-Open No. 45678/1991); (4) an adhesive which comprises polyvinyl alcohol, an aqueous emulsion, a crosslinking agent such as aluminum chloride and a polyvalent isocyanate compound (Japanese Patent Publication No. 16150/1982); and the like.
Nevertheless, in the above-mentioned adhesive (1), the crosslinking agent is not specifically exemplified and there exists the problem of the workability due to the short pot-life of the composition. The adhesives (2) and (3) have the disadvantage that the films obtained therefrom is low in wet strength. The adhesive (4) has the problem of the workability due to the short pot-life thereof.
Under such circumstances, the present invention has been contrived for the purpose of providing an emulsion composition which is favorable in workability due to a long pot-life and can be made into a film having a high wet strength and being excellent in water resistance, hot water resistance and heat resistance, said film being obtained by coating said emulsion composition and thereafter evaporating the water contained therein.